This article is about the structure itself. For the block required to activate the structure, see Nether Reactor Core.

The Nether Reactor is a man-made structure which, when activated, generates a massive 35×17×17 structure of netherrack with multiple floors, unofficially called a "Nether Spire".[1] It also turns the reactor itself, excluding the core, into glowing obsidian. At this point the reactor will begin to spawn various blocks and items, as well as zombie pigmen, provided the difficulty is at Easy or higher.

It is built with a nether reactor core, 4 gold blocks, and 14 cobblestone, arranged in the configuration above.

The Nether Reactor cannot be used in Creative mode.

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When the nether reactor is built and the core activated (by tapping), there will be a Client message that says, "Active!", and it generates a multi-floor structure of netherrack (35×17×17) unofficially called a "Nether Spire". It destroys any block that happens to be in the way of the spire. The blocks that make up the reactor, excluding the core, will turn into glowing obsidian.

In addition, it will start spawning various items and blocks. These can be gold ingots, melon seeds, paintings, glowstone dust, wooden doors, both types of mushroom, bones, cacti, arrows, sugar canes, bowls, beds, bows, pumpkin seeds, and nether quartz as well as zombie pigmen. Due to this great variety of items, it is advisable to empty out one's inventory beforehand so that no items are missed, other than any weapons used to fight the zombie pigmen (unless playing in peaceful difficulty). After it burns out, the massive netherrack structure with multiple floors will have many holes in its walls. The bottom floor is hollow (all blocks inside other than the reactor are replaced with air), and the upper floors retain the blocks that were already there (air for an above-ground spire, dirt/stone/etc. for an underground spire). The core is still there, and is reusable. The used core is found in a 3×3×3 obsidian box where the reactor was constructed. When the reactor is active, the core's texture will change to red, and after it burns out, it will change to a blackened texture which is very similar to obsidian and some players may even mistake the core for having turned into obsidian.

The nether reactor only lasts around 45 seconds. During the 45 seconds the reactor is active, it is easy to escape the room, as it is all netherrack. Once about 5,10, or 15 seconds have passed, the time sets to nighttime, so left over items in the room can despawn once the nether reactor stops.

The zombie pigmen who spawn are hostile to the player, and will burn (though not get hurt) in sunlight, unlike the ones in the PC or console editions. Their texture and animations are also slightly different. When a zombie pigman is killed it drops feather(s) and gold ingot(s), allowing you to multiply your gold source if you recover the blocks.

If it fails, for example if the design is incorrect; it sends a message into the chat to alert you.

The nether reactor doesn't only spawn nether items when activated, it also spawns other items, such as seeds.

The structure created by the reactor, the Nether Spire, is 17×17 blocks at its widest (bottom) and is 35 blocks high (2 blocks low and 33 blocks high).

The Reactor does not currently function in Creative mode; this is intended.[1]

When building the reactor, if the core is placed but the rest of the reactor is unfinished, text will appear onscreen saying "Not the correct pattern!".

Once the reactor is turned on, more text will appear, this time just saying, "Active!"

The reactor's structure was originally iron and gold blocks rather than cobblestone and gold, but this was changed due to its cost and the fact that the reactor turns everything into obsidian except the core.[2]

The air blocks in the pattern are not optional. This means the player cannot build the reactor underwater unless you waterproof the air blocks in the pattern.

The player can quickly mine some or all of the materials out of the reactor after activation and it will still function. This way the player can recycle the expensive gold blocks. Another alternative method is to simply have someone else help mine the blocks right after activation. If they're fast enough, they'll have time to mine all four gold blocks with a diamond pickaxe before they turn to obsidian.

If the player constructs the reactor near a world edge and activate it, they will see it turn night.

There is an elevation limit for the reactor, above which it cannot be activated.

If the player mines the active core, the glowing obsidian will not turn into normal obsidian.

The spire always generates with the same orientation.

If the player builds a reactor around the burnt out core, the spire will generate, but no items or zombie pigmen will spawn, the cobblestone and gold blocks do not turn into glowing obsidian, and the core remains in its activated state unless mined, making a netherack farm.

The ONLY block the nether reactor can't destroy is the "invisible bedrock" on the world edge, mainly because it breaks the netherrack before it spawns.

However, if you inventory edit it into your inventory and place, it will consume it.

If a Nether reactor is manually deactivated, nighttime will be eternal, unless one goes to sleep, but daytime would only last about 20 seconds, and quickly fade back to nighttime. This would also cause hostile mobs to stop spawning (but already spawned hostile mobs will remain). This can be easily fixed by ending the server and starting up again.

If you activate a nether reactor close enough to the bottom layer of the overworld, it can replace the bedrock with netherrack, giving access to the void in survival mode. If you do this it will say all players need to be near the reactor, even if you are single player mode. A fix for this is to activate it from one block higher.

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